Delta-9-tetrahydrocannabinol or Delta-9 THC, the principle active component of Cannabis sativa (marijuana), is a member of a large family of lipophilic compounds (i.e., cannabinoids) that mediate physiological and psychotropic effects including regulation of appetite, immunosuppression, analgesia, inflammation, emesis, anti-nocioception, sedation, and intraocular pressure. Other members of the cannabinoid family include the endogenous (arachidonic acid-derived) ligands, anandamide, 2-arachidonyl glycerol, and 2-arachidonyl glycerol ether. Cannabinoids work through selective binding to and activation of C-protein coupled cannabinoid receptors. Two types of cannabinoid receptors have been cloned including CB-1 (L. A. Matsuda, et al., Nature, 346, 561-564 (1990)), and CB-2 (Munro, S. et al., Nature, 365:61-65 (1993)). The CB-1 receptor is highly expressed in the central and peripheral nervous systems (Glass, M. et al., Neuroscience, 77:299-318 (1997)), while the CB-2 receptor is highly expressed in immune tissue, particularly in spleen and tonsils. The CB-2 receptor is also expressed on other immune system cells, such as lymphoid cells (Galiegue, S. et al., Eur. J. Biochem., 232:54-61 (1995)). Agonist activation of cannabinoid receptors results in inhibition of cAMP accumulation, stimulation of MAP kinase activity, and closure of calcium channels.
There exists substantial evidence that cannabinoids regulate appetitive behavior. Stimulation of CB-1 activity by anandamide or Delta-9 THC results in increased food intake and weight gain in multiple species including humans (Williams et al., Psychopharm., 143:315-317 (1999)). Genetic knock-out of CB-1 result in mice that were hypophagic and lean relative to wild-type litter mates (DiMarzo et al., Nature, 410:822-825 (2001)). Published studies with CB-1 small molecule antagonists have demonstrated decreased food intake and body weight in rats (Trillou et al., Am. J. Physiol. Regul. Integr. Comp. Physiol., R345-R353 (2003)). Chronic administration of the CB-1 antagonist AM-251 for two weeks resulted in substantial body weight reduction and decreased adipose tissue mass (Hildebrandt et al., Eur. J. Pharm., 462:125-132 (2003)). There are multiple studies that have assessed the anorexic effect of the Sanofi CB-1 antagonist, SR-141716 (Rowland et al., Psychopharm., 159:111-116 (2001); Colombo et al., Life Sci., 63:113-117 (1998)). There are at least two CB-1 antagonists in clinical trials for regulation of appetite, Sanofi's SR-141716 and Solvay's SLV-319. Published Phase IIb data reveal that SR-141716 dose-dependently reduced body weight in human subjects over a 16 week trial period. CB-1 antagonists have also been shown to promote cessation of smoking behavior. Phase II clinical data on smoking cessation were presented in September of 2002 at Sanofi-Synthelabo's Information meeting. This data showed that 30.2% of patients treated with the highest dose of SR-141716 stayed abstinent from cigarette smoke relative to 14.8% for placebo.